1. Field of the Invention
The invention relates to a direct radiation loudspeaker of the type conventionally comprising a mobile diaphragm attached by its outside edge to a rigid chassis forming a frame. It relates more particularly to an improvement for adapting the directionality of this kind of loudspeaker and more particularly for reproducing the directionality of a rectangular piston. One benefit of the invention lies in the fact that adapting the directionality of this kind of loudspeaker eliminates interference over an extended range of frequencies and thus enables a plurality of direct radiation loudspeakers to be coupled together.
2. Description of the Related Art
A conventional direct radiation loudspeaker comprises a mobile diaphragm that is relatively rigid and light in weight and has a conical, exponential or other cross section, at the center of which is mounted a coil adapted to move inside a magnetic field generated by a magnet. The mobile diaphragm is attached by its outside edge to a rigid chassis forming a frame which also supports the magnet. The frame coincides with a plane that is referred to hereinafter as the acoustic emission plane, beyond which sound propagates in the external medium. This kind of loudspeaker is one of the most widely used components in the art of sound reinforcement. An electrical signal representative of the sound to be reproduced is applied to the terminals of the coil, which moves in the airgap of the magnet. This movement entrains the diaphragm, which radiates acoustic energy toward the external medium, beyond said acoustic emission plane. This kind of loudspeaker has the following characteristics:                if the contour of the frame defined above is circular, the acoustic radiation from the loudspeaker is axisymmetrical, i.e. identical in all planes containing the axis of the loudspeaker, which is also the axis of the mobile coil.        The dispersion of the loudspeaker decreases as the frequency increases.        